Communications networks such as optical networks often employ error correction. Such optical networks typically use wavelength division multiplexing (WDM) or dense wavelength division multiplexing (DWDM) to increase transmission capacity. In WDM and DWDM networks, a number of optical channels are carried in each fiber at disparate wavelengths. Network capacity is based on the number of wavelengths, or channels, in each fiber and the bandwidth, or size of the channels. In WDM, DWDM and other optical networks, arrayed waveguide gratings (AWGs), interleavers, and/or fibergratings (FGs) can be used to add and drop traffic at network nodes and to multiplex and demultiplex traffic at network nodes. To enable reconfiguring the wavelength paths to be dropped or added at different nodes, network nodes having optical switches can be provided, known as all optical ROADM (Reconfigurable Optical Add Drop Multiplexer) nodes.
It has been appreciated that DWDM does not provide its own overhead for management nor protection schemes to recover from equipment failures. DWDM involves more network elements than earlier point to point optical links. Such elements, such as-optical amplifiers, multiplexers, and demultiplexers—and dispersion compensation units, can bring reliability concerns and warrant monitoring. As a result, the G.709 Optical Transport Network, or OTN standard was generated by the International Telecommunication Union Telecommunication Standardization (ITU-T) to provide management functionality for DWDM optical networks. OTN involves adding a frame of overhead information, (also called a digital wrapper), some to the front of the signal as a header, and some such as FEC (Forward Error Correction) as a trailer appended to the rear. The FEC can extend optical span distances by reducing bit error rates (BERs).
FEC is one of the most attractive features provided by G.709 Hierarchy. It allows the receiver to detect and correct errors and therefore permits the transmission of data along “disturbed” paths or to reach a longer distance than an equivalent signal without this feature. Therefore the FEC can improve the quality of the transmission but its deployment has a cost.